Sound producing device



March 2Q, 1945. w. c. EAVES 2,371,960

SOUND PRODUCING DEVIC Filed Jan. 1, 1942 3 Sheets-Sheet 1 BYWMOMATTORNEY March-2o, 1945. w C. EAVS 2,371,960

SOUND PRODQCING DEVICE Filed Jan. 1, 1942 s sheets-sheet 2v ATTORNEYMau'chy 20, 1945. w. c. EAvEs 2,371,960

SOUND PRODUCING DEVICE' ATroRN'EY vilatentedMar. 20, 1945 i unirse.STATES PATENT? FFICE SoUNn rnoDUcING DEVICE william c. naves, Elyria,om, signor to raves Sound Projectors, Inc., New York, N. Y., acorporation o! Delaware' Y Application January 1, 1942, Serial No.425,368A

I Claims. (Ci. 179-108) This invention relates to sound lproducingdevices and more particularly to devices of this character which employa modulated uid stream as the sound generating medium.

vOne of the objects of the present invention is to -provide novel meansfor modulating the stream of fluid passing through a fluid i'low typesound producing unit whereby sound reproduction of greater iidelity andgreater volume can be obtained by-said unit Vthan has` heretofore beenpossible in devices of this type Operating at like input pressures.

Another object of the invention is to provide novel pressure responsivemeans for balancing the' control valve of a pneumatic sound projectingdevice.

A furtherA object is to providenovel means for operatively connectingthe actuating mechanism of a iiuid ow sound producing unit with thevibrating fluid modulating element thereof.

Still another object is to provide a novel sound head for a reproducingmit wherein substantially all resonant frequencies, foreign to thefrequency band being reproduced, are eliminated.

A still further object is to provide a novel grid valve for modulatingthe fluid ow in a sound vproducing device and novel means for pivotallymounting the movable element of said valve.

` acters refer to like parts throughout the several views,

Fig-11s of one type of soundhead embodying the present invention; v jFig. 2 isy an enlarged sectional view taken substantially along line 2-2of Fig. r1 and having parts thereof shown in elevation:

- Fig. 3 is a fragmentary sectional view of a portion ofthe apparatusshown in Fig. 2, the cover of the housing for the actuating mechavnisrnof said apparatus being removed,i

Fig. 4 is a fragmentary view in side elevation of the portion of theapparatus shown in Fig. 3; Fig. 5 is a sectional'view, with parts brokenaway, taken substantially along line 5-5 of Fig. 3;

of the sound head and therefor; l

Fig. 7 is an enlarged view in side elevation of said mounting spring; il

Fig. 8 is a sectional view, rwith parts broken the mounting Spring away,of a form of heating unit utilized in the A further object is to providenovel adjuststream to -produce the sound wherein diil'erences .in theinput pressure of the fluid stream have substantially no effect upon thefidelity of sound reproduction.

The above and further objects and .novel features of the invention willmore fully appear from the following detailed description when the sameis .read in connection with thev accompanying' drawings. 'It is to beexpressly understood, however. that the drawings are for the purpose ofillustration only and are not intended as a dennition of the limits ofthe invention. reference for the' sound head, the section being takensubstantially'along line 8-8 of Fig. 1;

Fig. 9 is a fragmentary sectional view similar to Fig. 3 of an alternateembodiment of the present invention, with parts thereof grammatically;and

Fig. 10 is a view similar other embodiment. i

According to the present invention, fluid under I pressure is causedtolflow through a sound head, and this stream of uid is modulated bynovel control means. The modulated fluid stream constitutes the mediumfor reproducing and amplifying sounds which have been converted bysuitable apparatus into mechanical vibrations 28 mounted thereon, saidcasing together with this latter purpose being hadprimarily to the lappended claims.

In the drawings, wherein like reference charand as such' havebeenimparted to the control means.

Referring to the embodiment of the invention illustrated in Figs. 1 to8, the sound head com-: prises a housing 26 (Figs. 1 and 2) having aiiuid.

passage 21 extending therethrough 'and a casing the wall of .saidhousing forming a chamber 29 for containing control apparatus to be morefully described hereafter. Housing 26 is preferably formed in twosections 26o, 2Gb (Fig. 2l joined by suitable means, Such 'as screws26o. A'source of iiuid pressure,v as. for example, an air coinpresserunit (not shown) comprising a pump and:-

a reducing valve Aor other means for maintaining. theuid outputA of the-pump ata substana view in elevation on a reduced scaleI Fig. 6 is aperspective View of the movable grid to Fig. 9 of still an- `or fa likealuminum alloy. i

tially constant pressure, is connected to passage A21. preferably bymans of a coupling member 30 threaded into the'upper end of saidpassage, the

1 bore of the latter being internally threaded at A suitable air'iilter32 is held between the inner end ofsaid coupling member and an internalshoulder 33 formed in the wall of passage 21, said iilter, as 'shown,comprising av pair of screen members 34. having disposed therebetween alayer 35 of fibrous material, such as porous felt.

To modulate the stream of air flowing through passage' 21, novel valvemeans of the grid type are interposed in the path of said stream, saidmeans comprising a stationary grid plate 33 (Figs. 2, 3 and 5) and amovable grid plate 31 shown mounted on the low pressure side of saidstationary plate for cooperation with the latter. Grid 36 is xed betweensections 26a and 28h of housing 2B to extend transversely across passage21, and is provided with a plurality of parallel slots or ports v3i!(Fig. 5), each of said slots having side Walls vwhich are substantiallyperpendicular to the parallel faces of the plate. Slots 38 areprefcrably equally spaced across the plate and the solid portions orbars 33a between said' slots are of a greater width than the width ofsaid slots, for example, twice the width ofthe latter.

Grid 31 (Figs. 5and 6) is also provided with a plurality of parallelslots or ports 39 having bars 39a therebetween, and said slots Yare ofsubstantially the same, length and width as slots 33 and are spacedacross said grid in a manner similar to the'spacing of slots 38 acrossgrid 38. Grid 31 is mounted so that slots 39 and slots 33 (Fig. 5) areparallel and in staggered relation to each other, each slot ot one gridbeing opposite a bar of the other grid and-being pref` V erably locatedmidway between the two adjacent v equally spaced laterally and taperinglongitudinally toward the free end of-grid 31. Y

It is desirable that the faces of grid plates 3B and 31 be. smooth andthat,"when valve 38, 31 is in closed or inoperative position, as shownin' Fig. the adjoining faces of said valve plates have good surfacecontact with each other.

ably honed and lapped .to obtain smooth, plane surfaces.. Moreover, inorder to avoid 'electrolytic action between the plates and preventcorrosion,

the plates are preferably formed from dissimilar'Y metals having a highresistance to corrosion. For

example, plate 33 may be formed from brass or German silverwhile plate31 is made of Dural .'rhetmcrer portion of plate- :1 extends through arecess 40 (Figs. 2 and 3) in theinnerendof.,

` l section 24h` and is mounted in a novel manner "".ln ychamber 23 bybeing formedas onaarm of an, L-shaped valve member 42, the other arm ofsaid ymember being numbered 43. Arm 43 is prei'- 1 erably perpendicularto plate 31 and comprises a base portion. 43a' (Flea. 4. and 6)vadjoiningslid Accord-' ingly, during fabrication, said plates arepreferof base 43a, saidy central portion being connected plate 'and anelongated lever portion 43h extending outwardly and centrally from saidbase portion.

Moisture condensed from the air stream in passage 21 if permitted topass into the chamber 23 tends to corrode or otherwise'impair theoperation of the .control and driving means in said chamber, and toprevent such an'occurrence recess 4i) has inserted in the wall thereof amember 40a (Figs. 3 and 4) of relatively soit, nonacter of the materialof pad 40a, the latter also acts to dampen any resonance eiects set upin `I -shaped member d2, thereby preventing a foreign frequency frombeing imposed on the voice or other frequencies being produced by theair stream.

To mount valve member 42 for substantially frictionless pivotalmovement, a thin, fiat member 44 is provided toserve as a torsion springsupport therefor. Member 44, which may be formed from spring steel, is'secured at theends thereof by suitable means, such as screws 45, to thewall of housing 26, and intermediate the ends thereof to base 43a,preferably by a pair of rivets 46. As shown, member 44 spans a groove 41(Fig. 4) provided in the wall of housing 28, said grooveextendinglengthwise beyond both sides of' base 43a. Spring 44 has enlarged endportions 44a for receiving screws 45 and a relatively wide centralportion 44h (Fig. 6) for engaging the face to said end Aportions byrelatively narrow strips 44o. It is preferable that the plane of portion44h have a slight inclination relative to the plane of portions 48a whenspring 44 is subjected to no external forces (Fig. 7) so that when vsaidportions are mounted to become coplanar, as shown in Fig. 3, grid 31 isbiased in the direction 'of grid 36o l To control the pivotal movementof valve member 42 and prevent undue distortion of spring 44, novelbearing means are associated with said member and spring to provide ailxed axis for said pivotal movement. As lillustrated, the bearing meanscomprise a pair' of pivot pins 48 (Figs. 3 and 4) embedded in orotherwise riga idly secured to the Wall of housingv 28 with the outer,pointedends 48a' (Fig. 3) thereof engaging the bottoms ot a pair ofrecesses 49 provided in the ends of rivets 46 (Fig. 6). It is to beunderstood that recesses 49 are not limited to location :in the ends ofthe rivets .but may be disposed at any -two points in the face of saidspring along the selected pivotal axis and that, if desired, more thantwo sets of pins and recesses disposed along said axis may be providedto serve as the fulcrum for said Spring. Moreover, pins 43 may bemounted for direct engagement with the flat face of spring 44 or rivetsd'may'have the heads thereof rounded for direct'engagement with the wallof houslng-26 so as to dispense with pins 43.

barrel.

member 63 between the end of portion 64 and a screw member 68, threadedinto the outer end a. flat, metal diaphragm 53, mounted across anopening 54 in the wall of housing 26 to com,- municate with chamber I,the latter being con.-

stituted by the portion of passage 21 between block 52 is thus effectiveto transmit to lever 43h pressures applied by diaphragm 53 in adirection t'o oppose movement of said lever to the left-as viewed inFig. 3l The provision o f a non-resonant link between diaphragm 53 andlever 43h prevents thetransmission of resonance vibrations from saiddiaphragm to valve member 42, and also acts as an additional pressurecompensating element.

'I'he eiective area of diaphragm 53 relative to the eflectivearea ofgrid plate 31, when the latter is in closed'\position, is such that thetorque .opposing the lpivotal movement in a counterbarrel 63 -tosecurely hold said barrel 'in axial adjustment.

When the relationship between the eective areas of diaphragm 53and gridplate 31 is such that 'the desired balance of valve member 42 is notattained, the'axial position of barrel 63 is ad.- ju'sted by asuitabletool so that pin 6I will apply tlie'desired pressure to thediaphragm to effect the proper balance. Pin 6|', or at least the headvthereof, is preferably formed from a relatively rigid, non-resonantmaterial, such as hardrubber, vto minimize the possibility of setting upresonant vibrations which are foreign -to the sound frequency beingreproduced.

AIn order to modulate the air stream flowing through passage 21 andvalve 36, 31 and impart 'desired sound producing characteristicsthereto,

controlled vibrations within the audible frequency range are transmittedto member 42 and-are, in turn, imposed on said air stream by grid plate31 of said member. For this purpose, suitable actuating means 10 aremounted in chamber 23, for example, by a bracket 10a shown in brokenlines (Fig: 2) andfasillustrated, said means comprise an electrical unitof the magnetic type having a U-shaped, permanent magnet 1i carrying avoice coil unit-12, the latter being adapted clockwise direction,.asviewed in Figs. 2 and-3, o f member 42 and applied by said diaphragm,is-V slightly less than the torque applied by the air under pressure inchamber 5 I to plate 31. This.

pivotal movement of member 42 is opposed not only by the air pressure onthe inner face of diaphragm 53 but also bythe deformation of springmember 44 and the diaphragm. The reincreases with an increase in thepivotal movement of member 42, While the forces acting on grid 31 due to.air flow and air pressure tend to decrease in magnitude as the distancebetween grid plates 36 and 31 increases. Accordingly,

at a point in the angular displacement of member 42, the resistingtorque becomes equal to the torque inducing the pivotal displacement andthe member is placed in equilibrium or is balanced,

whereupon the slightest vibration applied to diaphragm 53 in order toincrease the resistancev to counter-clockwise pivotal movement o fva'lve member 42 when'such increase-isinecessaruto` properly balancesaid member.- As shown. said means comprise a pin 6l slidably mounted inthe inner portion 62 of the bore of an externally threaded barrel 63which extends through a threaded opening in the wall of housing 26.Pinvv 6i, which projects b'eyond the inner end of the Y barrel, has aheadportion 64 of enlarged diamef-fAv ter which engages an internalshoulder 65' insaid A spring 61 is positioned inthe bore of of barrel63. Spring 61 urges the shoulder on A pin 6| into engagement;with-shou1der65and the.

pin intovengagement with the inner face of diaphragm 53, lthepressure-applied by said spring being subject to control by the axialadjustment Y.

The barrel and pin are.

to respond to current modulations to produce vibrations in an armature13 corresponding to said modulations.' Armature 13 is mounted to havethe longitudinal axis thereof substantially parallel to grid 31 and isvibrated by said actuating means in a direction perpendicular to itslongitudinal axis. `It is to be understood that other types of actuatingmeans capable of imparting controlled vibrations to a movable arm.

such as armature 13, may be utilized instead of l' the magnetic voicecoil unit 1l, 12;

sistance provided by spring 44 and diaphragm 53 40' To faithfullytransmit the vibrations from actuating means 10 to grid 31 and therebyattain s ound reproduction of high fidelity, a novel connecting linkageis provided between member 42 and said means. As shown, the linkagecomprises armature 13 and an element 14 rigidly vsecured at oneendthereof to said armature to extend therefrom at an angle ofapproximately in the direction of member 42, said element being securedat the other end thereof to an arm 15 formed with or otherwise rigidlyfixed to arm 43 of the valve member, for example, .bg

being threaded therein. A pair of nuts 16 are in -Y threaded engagementwith the externallg threaded portion 15a. of arm 15, and link 14 ilpreferably secured to said arm by having the end thereof clamped betweensaid nuts. Arm Il is mounted so that the extension of the longitudinalaxis thereof passes through the center of mass of member 42 andintersects the pivotal axis of. said member as determined bybearings 48,49.:

It is preferable to mount arm 15 perpendicular" to lever 43 and,accordingly, the 'pivotal axis of` Ymember 4-2 is located in a planewhich is parallel f to movable grid 31and'which contains the center o f`mass of. said member. As a Vresult` ofthis member and theprobability ofsetting upint'erfeing resonant vibrations in the parts of saidmountingLof 'arm 15 and member 42, a balancedcondition may be morereadily imparted to `said member during operation is greatly minimized@lThe modulated air iiowing from valve 36, 31v

passes through th'oatportionlof passage 21. to a suitable soundpropagating device,` such asa horn (not shown), which lmay be mounted ontheexternally threaded lower -end of section 2Gb (Fig. 2). However, asthe entire volume of air der the sound head' inoperative.

:lowing through stationary grid 38 cannot be connection to said memberfrom the actuating subjected to the modulatingeiiects of movable grid31, some air iiowing past the edges .of the latter as straight jets, athroat 11 is formed to offer a maximum amount o! influence on theseunmodulated straight Jets and, in the illustrated embodiment, saidthroat is constricted in somewhat the same manner as the throat portionof a Venturi tube, lbeing proportioned to dissipate the energy of thecurrents of unmodulated air and thereby preventing said currentsfromilow ing to the horn as straight jets with ensuing hissing noises.

The formation of ice on the surfaces of grids 38 and 31 or on the wallsof the portions oi' passage` 21 adjacent said grids seriously aiects thequality oi' the sound reproduction and may ren- Accordingly, suitablemeans for preventing theformation of ice on the wallsof passage 21 andon the surfaces ci plates 38 and 31 are provided, and in one formcomprise a substantially cylindrical container 19 (Figs. 1 and 8)lformed with housing 28 in the lower end of section 28a of said housing,said container having an open end and a flange 80 formed at said end. Anelectrical heating 'assembly 8| is positioned in container 19 throughthe open end of the latter, and is connected by suitable means, such asa cable 82, to a source of electrical energy (not shown), said cablehaving an annular, transversely disposed disc 83 secured thereon andadapted to be xed to ange 88 by means of screws 8l. Heat generated inheating assembly 8l is conducted to valve 88, 31 and the adjacent wallsof passage 21 to maintain the parts at a temperature exceeding thefreezing temperature of water. arrangements may also be utilizedfor thepurpose of preventing ice formation; for example, a heating assembly maybe located on the interior o! housing 28 in chamber 5i, or a heatingelement may be mounted in contact 'with stationary grid 38 adjacent thewalls of passage 21.

During the operation of the above-described air head, it is desirablethat the pressure ofthe fluid admitted to passage 21 be maintained at aconstant value. The pressures available for operation oi the unit rangefrom pressures suiiicient onlyto produce an air stream through the airhead, e. g., pressures less than 3 lbs. per sq. in. gauge, to pressureslimited only by the structural resistance of the parts of the unitdirecting and controlling the air stream. I'he fidelity of soundreproduction obtained by the sound head is sub-` stantially unailectedfor cooperating pressure selected' from the range of pressures between 3lbs. per sqin.- gauge and 45 lbs. per sq. in. gauge,

the higher operating pressure having the eiiect.,l

means, is shown in Fig. 9. The iiow o! iluid through passage 21is'modulated'by a valve comprising statonary'grid -38 and a movable grid85 cooperating with the stationary grid to pei'-l form the same functionas plate. of Figs. 1 to 8. However, grid 88 is disposed on the highpressure side of grid 38 rather than on the low pressure side, as inthefirst embodiment. and extends through a recess 88 in the lower end ofhousing section 26a, said recess being suitably lined with a layer 81 ofrelatively soft, non-resonant material, such as sponge rubber. Ifdesired, grid 85 may be pivoted at the left hand end thereof to housingsection 28a, or said grid may be floated inoperative position merely byits connection to armature 93 to be described hereafter, but preferablysaid grid85 forms one arm of a valve member 88, which is pivotallymountedon the exterior of passage 21 by a torsion spring 89 similar tospring Il, spring 89being initially deformed, however, to apply acounter-clockwise torqueV (as viewed in Fig. 9) to member 88.

Other heating Pressure responsive unit 58 is connected by formed withmember 88 so as to apply a clockwise torque to the latter when actuatedby pressures in chamber 5l. The eiective pressure are! of the diaphragmof said unit relative to the aren of grid 88 is such that the admissionof air, or other uid, under pressure to chamber 5i causes said unit toapply a sufiiciently greater torque to member 88 than is applied theretoby the pressure of the air on grid to pivotA said member clockwise andmove grid 85 away from stationary grid 36. The differential torqueproducing Ythis pivotal movement decreases as the magniat, a suitablepoint in the displacement of said of producing a greatervolurne ofsound. Chamber 5| on the high pressure side of valve 86, 31

is of sufllcient'cross-sectional. area and volume to exceed the flowcapacity of said valve at any given pressure of entering' iiuid.Accordingly,

member.

It is to be understood that suitable means, such as compensating means80 (Fig. 3), for applying an additional force tendingl tobalance'memberl88 may be provided in the unit.of Fig. 9 if properbalance cannot be otherwise attained, as for example at a low operatingpressure.

To impart vibrations to member 88 and thereby modulate the air stream inpassage 21, electromagnetic actuating means 9i are provided, and. areshown diagrammatically in Fig. 9 as comprising a magnet 82 and a voicecoll 92a. To transmit vibrations to valve member 88 in accordance withmodulations in the current passing through coil 92, anelement 93 isintegrally formed with or rigidly secured to said valve member 88 and ismounted to be substantially parali'lel to'grid 85 and to extend inl thedirection of said chamber acts as a reservoir for the uid stream andmaintains the air pressure' adjacent the high-.pressure side of valve38, 31 substantial'ly constant while a continuous stream of air flowsthrough said valve. Grid 3,1 Ais balanced. in theair stream by pressureresponsive means 58, compensating;meansv 88 and spring 44, and.

is vibrated by actuating means 10 to impart sound producing modulationsto said stream.

Another embodiment of the invention, includv ing an alternate mountingarrangement for the movable grid 'of the control valve anda novelactuating. means 9i. The free Vend oi said element is located in themagnetic eld of sad actuating means to serve as the armature thereofand, accordingly.. provides for the directl transmission of vibrationsfrom said-actuatingimeans to the movable valve member.

Still anotherl embodiment of the present invention is shown in Fig. 10and comprises a heusing having-a iluid passage formedtherein. Valvemeans corresponding instructure to valve means 88, l2 of the embodimentof'Figs. f to 8 are provided for modulating-a duid streamflowingfthroughsaid passage, and comprise a stotionary grid 01 and a movable member 08havi118 grid 99 formed therewith. Valve member 08 is pivoted on atorsion spring mounted and In order to actuate movable grid 99 and im'part-controlled vibrations to the latter, a lever or arm |02 is formedwith or otherwise rigidly secured to said plate at the end thereofremote from the pivotal axis, said lever extending through a recess |03in housing 9-4. A layer |04 of non-resonant material, 4such as spongerub-` ber, may be provided in a groove inthe walls of said recess toengage and form a substantially fluid-tight seal with the side andbottom faces of said lever. The free end of lever |02 is'actuated bysuitable electromagnetic means comprising a magnet |06 and a voice coil|01, said lever constituting the armature of said means. This novelarrangement provides a direct connection between the actuating meansandthe vibrating valve member so that the vibrations are transmitted tothe latter through a minimum mass of material whereby sound reproductionof a great.- er fidelity and superior tonal qualities may be -obtainedby the unit embodying" this structure.

There is thus provided a novel sound reproduc-l ing unit of the fluidflow type, i'. e., of the-type utilizing a modulated fluid stream,preferably` anv air. stream, as the sound generating medium. The

novel sound head comprises valve means for modulating a uid current, andnovel means responsive to the pressure of the fluid current for applyinga balancing torque to the movable member of saidvalve means. A novelvibration transmitting linkage operatively connects the movable memberof the valve with the actuating means, and novel means are provided forpreventing the formation of ice in or 'on said unit where such formationwould cause improper operation of said unit and for preventing moisture,which condenses from the fluid stream, from ilowing to the control andactuating apparatus mounted exteriorly of the fluid flow passage. Othernovel Y means embodied in the present invention are operative to preventthe creation of" resonant vibrations in the parts of the unit connectedto the control member and to thus maintain a high fidelity of soundreproduction. The movable member of the grid type, fluid modulatingvalve is mounted in a novel manner so' as to be readily pivoted by thefluid stream to an equilibrium position, in which position said memberis extremelyisensitive to vibrations imparted thereto by the actuatingmeans.

Although several embodiments of the inven- Y tion have been illustratedand described, it is to be expressly understoodtiat' the samefis notlimited thereto. The ,.fflatdlhphragm, which constitutes thepressureresponsive element of the balancing means, may be replaced byother ele-y 'ments ormeans responsive to pressure differentialsexistingV between opposite sides or faces thereof. Various other changes.may be made in the design and arrangement of parts with--outldepa'rting from the spirit and scope of thev invention. For a.definition of the invention, reference will be had primarily to theappended claims. a A

What is claimed is: y l. In a sound reproducing unit utilizing an airstream as the sound generating medium, the' combination with controlmeans for modulating the air stream including valve means of the gridtype having a movable member in the path of said air stream, of meansactuated bythe pressure of s said air stream for applying a balancingforce to said movable member opposed to the lforce exerted thereon bythe uid stream, and springpressed means for augmenting the balancingforce applied by said pressure actuated means, l0 said spring-pressedmeans and said pressure actuated means being so arranged andproportioned relative to said member as to lbalance the latter in openposition in said stream.

2. In a sound head of the fluid flow type havn ing valve means forimparting modulations to a duid stream, the combination therewith 'ofmeans `for balancing said valve means in open position in said fluidstream, vsaid balancing means comprising a mechanism `actuated by the .wpressure of the fluid vstream for en'gagingand applying a balancingforce to said valve means, and a spring-pressed, non-resonant memberadapted to engage said mechanism during the movement of said valve meansto open position to augment the balancing force applied by saidmechanism. y i

3, In a sound head adapted Ito reproduce sounds by means of a modulatediiuid stream, valve means in the path of said fluid stream for nmodulating the latter, means for balancing said d valve means in openposition in said fluid stream to render said valve means accuratelyresponsive to actuating vibrations, and means connecting valvemeans inthe path of said stream, for modulating the latter, and means forbalancing sas-l valve means in open position in said nuid stream torender saidvalve means accurately responsive to actuating vibrations,said balancing means comprising a mechanism disposed substantiallyparallel to the fluid stream and actuated by the .pressure of the uidstream for engaging and applying a balancing force to said valve means60 and a spring-pressed non-resonant member adapted to engage saidmechaf mqduring the movement of said valve means "op'en position Itoaugment the balancing force appliedby said K mechanism.

comprising a fluid passage, valve means for conl trolling a fluid streamproduced 'by the admission into said passage of a fluid under pressure,said valve means comprising a. stationary-grid and a movable gridmounted on the low pressure side U ofv said stationary grid, a memberrigidly secured to said movable grid, means for-fpivotally mounting saidmember on the exterior'of said passage,

said: last-namedmeans comprising a torsion 35 spring secured to saidmember, said spring urgv ing said movable grid toward closedposition,balancing means including an element responsive to the differencebetween the pressures on` y the interior and exterior of. said passage,and a applying torques to' said member balancing said grid in the fluidstream.l

76 6. In soundreproducingfapparatus of the type said balancing means tosaidvalve means, said l 5. In apparatus of the class described,meanslinlr of non-resonant material' operatively connecting said.pressure responsiveelementto said member, said balancing means and saidspring `having a movable grid member for modulating a uid stream inresponse to the movement of a vibratingv armature, a resilient elementattached i to said member and having acentral portion inf.

. clined relative to the plane of the end portions having a movablevalve member tor modulating a uid stream in accordance with the movement*of a vibrating armature, means for 'pivotally mounting said member-forangular movement v l about a xed axis. and means for operativelyconnecting saidarmature to said member to actuate the latter, saidconnecting means comprising a link rigidly lsecured to said member. andmeans for transmitting the vibration of said armature to said link in adirection perpendicularA to the longitudinal-'axis of said link, thelatter `being mounted to have the longitudinal axis thereof pass throughthe center ot mass of said member-at an angle of 90 tothe pivotalv axisof 15 the latter.

WILLIAM c. naves

